Technical Field
This invention relates to a pen-shaped coordinate indicator that indicates a position to be detected to a position detecting device and that supplies operational information to the position detecting device.
Description of the Related Art
In recent years, a position input device is used as an input device such as a tablet PC (personal computer). A position input device is composed of, e.g., a coordinate indicator formed in a pen shape (pen-shaped coordinate indicator) and a position detecting device having an input surface, to which pointing operation and input of characters, figures, etc. are performed by using a pen-shaped coordinate indicator. FIG. 21 shows one example of the schematic configuration of a pen-shaped coordinate indicator 100 and a position detecting device 200 of a related art.
As shown at the upper left part of FIG. 21, the circuit configuration of a pen-shaped coordinate indicator 100 has a first ferrite (ferrite chip) 102 and a second ferrite (ferrite core) 104. Furthermore, at least one resonance capacitor 115 is connected to a coil 105 wound around the second ferrite 104. In FIG. 21 two resonant capacitors 115a and 115b are connected to the coil 105.
More specific configuration of the pen-shaped coordinate indicator 100 is shown in FIG. 22. FIG. 22 is a sectional view of the pen-shaped coordinate indicator 100 and shows the state in which the coil 105 is wound around the second ferrite 104. As shown in FIG. 22, the pen-shaped coordinate indicator 100 has a configuration in which the first ferrite 102 and the second ferrite 104, around which the coil 105 is wound, are made to oppose each other with the intermediary of an O-ring 103. Furthermore, it has such a configuration that application of pressing force (writing pressure) to a core body 101 brings the first ferrite 102 closer to the second ferrite 104.
The O-ring 103 is a ring-shaped member formed of synthetic resin, synthetic rubber, etc. to have a shape of the alphabet “O” (circular shape). Furthermore, in the pen-shaped coordinate indicator 100, besides the above-described parts, a board holder 113, a board 114, a resonant capacitor 115, a ring-shaped film 117 as a buffer material, and a buffer member 118 are housed in a hollow case 111, as shown in FIG. 22. Their positions in the case 111 are fixed by a cap 112. A resonant circuit 116 is configured by connecting the coil 105 wound around the second ferrite 104 to the resonant capacitor 115.
When the first ferrite 102, against which the core body 101 forming the pen tip abuts, gets closer to the second ferrite 104 according to the pressing force applied to the core body, the inductance of the coil 105 changes correspondingly. As a result, the cycle (resonant frequency) of the oscillation of radio waves transmitted from the coil 105 of the resonant circuit 116 changes.
On the other hand, as shown in FIG. 21, the position detecting device 200 has a position detection coil 210 obtained by stacking an X-axis-direction loop coil group 211 and a Y-axis-direction loop coil group 212. The respective loop coil groups 211 and 212 are each composed of forty rectangular loop coils, for example. The respective loop coils configuring the loop coil groups 211 and 212 are so disposed as to be arranged at equal intervals and sequentially overlap with each other. These X-axis-direction loop coil group 211 and Y-axis-direction loop coil group 212 are connected to a selection circuit 213. The selection circuit 213 sequentially selects one loop coil among the two loop coil groups 211 and 212.
An oscillator 221 generates an alternate current signal, namely, AC signal with a frequency f0 and supplies it to a current driver 222 and a coherent detector 229. The current driver 222 converts the AC signal supplied from the oscillator 221 to a current and supplies it to a transmission-side terminal T of a switch connection circuit 223. The switch connection circuit 223 switches the connection target of the loop coil selected by the selection circuit 213 to either the transmission-side terminal T or a reception-side terminal R under control from a processing controller 233 to be described later.
Suppose that the loop coil selected by the selection circuit 213 is connected to the transmission-side terminal T of the switch connection circuit 223. In this case, the AC signal from the oscillator 221 is supplied to this selected loop coil via the current driver 222 and the transmission-side terminal T, to be transmitted to the pen-shaped coordinate indicator 100.
On the other hand, suppose that the loop coil selected by the selection circuit 213 is connected to the reception-side terminal R of the switch connection circuit 223. In this case, an induced voltage generated in the loop coil selected by the selection circuit 213 is supplied to a receiving amplifier 224 via the selection circuit 213 and the reception-side terminal R of the switch connection circuit 223. The receiving amplifier 224 amplifies the induced voltage supplied from the loop coil and supplies it to a detector 225 and the coherent detector 229.
The detector 225 detects the induced voltage generated in the loop coil, i.e., a reception signal from the resonant circuit of the pen-shaped coordinate indicator 100, and supplies it to a low-pass filter 226. The low-pass filter 226 has a cutoff frequency sufficiently lower than the above-described frequency f0. It converts the output signal of the detector 225 to a direct current signal, namely, DC signal and supplies it to a sample/hold circuit 227. The sample/hold circuit 227 holds the voltage value of the output signal of the low-pass filter 226 at predetermined timing, specifically at predetermined timing in the reception period, and supplies it to an A/D conversion circuit 228. The A/D conversion circuit 228 converts the analog output of the sample/hold circuit 227 to a digital signal and supplies it to the processing controller 233.
The coherent detector 229 generates two orthogonal signals (0° and 90° from the AC signal from the oscillator 221 and multiplies the output signal of the receiving amplifier 224 by the generated signals to detect the phase difference. A low-pass filter 230 has a cutoff frequency sufficiently lower than the frequency f0. It converts the output signal of the coherent detector 229 to a DC signal and supplies it to a sample/hold circuit 231. The sample/hold circuit 231 holds the voltage value of the output signal of the low-pass filter 230 at predetermined timing and supplies it to an A/D conversion circuit 232. The A/D conversion circuit 232 converts the analog output of the sample/hold circuit 231 to a digital signal and supplies it to the processing controller 233.
The processing controller 233 controls the respective units of the position detecting device 200. Specifically, the processing controller 233 controls selection of the loop coil in the selection circuit 213, switch of the switch connection circuit 223, and the timing of the sample/hold circuits 227 and 231. The processing controller 233 causes radio waves to be transmitted from the X-axis-direction loop coil group 211 and the Y-axis-direction loop coil group 212 for a certain transmission continuation time.
An induced voltage is generated in the respective loop coils of the X-axis-direction loop coil group 211 and the Y-axis-direction loop coil group 212 by radio waves transmitted from the pen-shaped coordinate indicator 100. The processing controller 233 calculates the coordinate values of the position indicated by the pen-shaped coordinate indicator 100 along the X-axis direction and the Y-axis direction based on the level of the voltage value of the induced voltage generated in the respective loop coils. Furthermore, from the result of the cycle (phase) detection of 0° and 90°, the processing controller 233 performs predetermined arithmetic operation to calculate the phase value and additionally calculates the writing pressure value based on the phase value.
In this manner, in the related-art position input device composed of the pen-shaped coordinate indicator 100 and the position detecting device 200, it is possible to detect not only the position indicated by the pen-shaped coordinate indicator 100 but also the pressing force applied to the pen-shaped coordinate indicator 100, i.e., the writing pressure. Details of the related-art pen-shaped coordinate indicator 100 illustrated in FIGS. 21 and 22 are described in Patent Document 1 shown below.
[Patent Document 1]
Japanese Patent Laid-open No. 2002-244806